In presentations where images are projected onto a screen using a projection device, such as a liquid crystal projector, and various presentations and explanations are given to an audience with reference to changing projected images, a laser pointer is often used to point out a specific part of a projected image. However, the laser light emitted by laser pointers is dangerous if it directly enters a human eye. Therefore, various safety measures have been proposed for preventing the laser light from being accidentally directly projected into the eye of someone in the audience. For example, Japanese Laid-Open Patent Application H10-04228 describes a laser presentation system using a laser pointer where projected laser light is automatically turned ON/OFF according to the brightness of the laser light projection object, such as a projection screen, and the laser light is projected only when the brightness exceeds a certain threshold value. However, using the safety measures described in that published Japanese patent application, depending on the illumination of the room, there may be places other than on the projection screen where the brightness exceeds the threshold value and the laser light might be projected to the audience in those places.
Additionally, Japanese Laid-Open Patent Application 2000-321530 describes a laser presentation system using a laser pointer where the angle of projected laser light in the vertical or horizontal direction is detected and the laser light is projected only when the angle is within a specified range. However, as described in that published Japanese patent application, depending on the arrangement of the audience, for example, when stadium seating or second floor seating is used, parts of the audience may be at projection angles where laser light is emitted, resulting in laser light directly reaching people in the audience. Also, in both laser systems described above, the configuration and settings required of the laser pointers may be complicated, thereby increasing costs of the laser presentation systems.
Also, Japanese Patent No. 2591667 describes a laser presentation system using a laser pointer with an infrared emitter placed, for example, on top of a projection screen and laser light projection of the laser pointer is only enabled when radiation from the infrared emitter is detected by the laser pointer. However, when the laser pointer is directed toward an audience, there is a possibility of a malfunction in which the laser pointer receives infrared radiation emitted from the infrared radiation emitter that is reflected by the projector or the audience. Also, because laser light is projected even when the presenter is located behind the projector, namely on the audience side of the projector, laser light may be projected to an audience member who is on the screen side of the presenter. Also, because the infrared radiation emitter is placed in the laser light projection direction, it is easily subjected to a limitation of locations where it can be installed, and thus its installation and the adjustment of the infrared radiation emission direction becomes difficult.
Additionally, Japanese Laid-Open Patent Application 2000-321531 describes a laser presentation system with a laser pointer where infrared radiation is projected from a laser pointer in the same direction as the laser light. Whether the infrared radiation is projected onto the screen or not is determined by an imaging device, such as a CCD, and only when the infrared radiation is properly imaged is a signal issued that enables laser light projection by the laser pointer. However, when the laser pointer is directed toward an audience, infrared radiation emitted by the laser pointer may directly hit a part of the imaging device and mistakenly be recognized as a reflection from the screen. Also, the scale of the system tends to be large and laborious adjustments of the system, such as positioning the imaging device relative to the screen, tend to make the system impractical. Also, in the same way as with the prior art system described immediately previously, because laser light is projected even when the presenter is located behind the projector, laser light may be projected to an audience member who is on the screen side of the presenter.
The present invention is related to laser presentation systems using a laser pointer that are of simple configurations and that prevent unsafe projection of a laser beam of the laser pointer directly toward an audience.